Wireless communication systems and networks are used in connection with many applications, including, for example, satellite communications systems, portable digital assistants (PDAs), laptop computers, and portable communication devices (e.g., cellular telephones). One significant benefit that wireless communication networks provide to a user of such an application is the ability to connect, or stay connected to, a network (e.g., the Internet) as long as the user is within range of the wireless communication network.
Three major access techniques have been developed which are used to share the available bandwidth in a wireless communication system. Two of these techniques are referred to as time division multiple access (TDMA) and frequency division multiple access (FDMA). In TDMA systems, two or more signals (e.g., voice or data signals) share a single channel. In particular, in TDMA systems, multiple signals are transmitted over the same channel by allocating to the transmission of each signal a different time interval. In FDMA systems, on the other hand, the available frequency spectrum is divided into narrow channels, where each signal to be transmitted is assigned to a respective channel. The third technique, which is most relevant to the invention and is described below, is referred to as code division multiple access (CDMA).
CDMA systems operate by dividing a radio spectrum to be shared by multiple users through the assignment of unique codes. CDMA systems assign a unique code to each signal that is to be transmitted, and are thereby able to spread many simultaneous signals across a wideband spread spectrum bandwidth. Using the respective codes, the signals can then be detected and isolated from the other signals that are being transmitted over the same bandwidth.
FIG. 1 is a simplified illustration of one embodiment of a CDMA wireless communication system 100 in which the present invention may be implemented. As the main features of wireless communication system 100 are well know to those versed in the art, only a brief description of its components will now be provided. Further explanation will be provided below as necessary to aid the understanding of the principles of the present invention described herein.
As shown, wireless communication system 100 includes a plurality of mobile subscribers (MSs) 101-109. Mobile MSs 101-109, which are also known as mobile stations, mobile nodes, and by other names, each function as an Internet Protocol (IP) client (Simple IP and/or Mobile IP, as explained below). MSs 101-109 may each be any suitable device that is capable of communicating with a wireless network, such as a cellular telephone or a laptop computer with a wireless modem.
Wireless communication system 100 also includes a plurality of base stations or base transceiver stations (BTSs) 111-113 for managing wireless links to MSs 101-109. BTSs 111-113 act as the interface between the network and MSs 101-109, in that they convert digital data into radio signals and vice versa. Although not shown, each of BTSs 111-113 generally has an associated radio tower or antenna and communicates with various MSs 101-109 using radio links. In particular, BTSs 111-113 communicate with various MSs 101-109 through the modulation and transmission of sets of forward signals, while BTSs 111-113 receive and demodulate sets of reverse signals from various MSs 101-109 that are engaged in a wireless network activity (e.g., a telephone call, Web browsing session, etc.)
As shown in FIG. 1, BTSs 111-113 connect to one or more base station controllers (BSCs) 121-122 (e.g., using un-channelized T1 facilities or direct cables, although this is not required). BSCs 121-122 are used to interface (aggregate) all radio frequency (RF) traffic arriving from the antennas of BTS 111-113, and to provide this traffic to a mobile switching center (MSC) 123. As known in the art, BSCs 121-122 are generally responsible for managing the radio resources for one or more BTSs 111-113. For example, BSCs 121-122 may handle radio-channel setup, frequency hopping, and handovers (which are described below). Moreover, MSC 123 is responsible for providing the interface between the radio access network (RAN), which includes BTSs 111-113, BSCs 121-122, and PCFs 131-132, and a public switched telephone network (PSTN). In particular, MSC 123 controls the signaling required to establish calls, and allocates RF resources to BSCs 121-121 and packet control functions (PCFs) 131-132.
PCFs 131-132 are used to route IP packet data between MSs 101-109 (when within range of one of BTSs 111-113) and packet data service nodes (PDSNs) 141-143. PDSNs 141-143, in turn, are used to provide access to one or more IP networks 151-153, which may be, for example, the Internet, intranets, applications servers, or corporate virtual private networks (VPNs). In this manner, PDSNs 141-143 acts-as an access gateway. Although not shown in FIG. 1, PDSNs 141-143 generally also act as a client for Authentication, Authorization, and Accounting (AAA) AAA servers. As known in the art, AAA servers are used to authenticate and authorize MSs 101-109 before access is granted to one of IP networks 151-153.
It will be understood that nine MSs 101-109, three BTSs 111-113, two BSCs 121, two PCFs 131-132, and three PDSNs 141-143 have been shown in FIG. 1 solely for the sake of adding clarity to the description of the present invention. Persons versed in the art will appreciate, however, that the invention is not limited by the particular number of these components that exist in wireless communication system 100. Moreover, it will be understood that, although not shown in FIG. 1, various MSs 101-109 may have radio connections with more than one of BTSs 111-113. Similarly, a single PCF 131-132 may support more than one of BSCs 121-133 in wireless communication system 100. Persons versed in the art will also appreciate that, although the invention is described with reference to PDSNs 141-143, the principles of the present invention discussed herein can be used with other types of network access servers (NASs). In particular, it should be understood that the invention is applicable to any current or future access technologies where MSs 101-109 use the point-to-point (PPP) protocol as a client access protocol with an access gateway.
As known by those versed in the art, two modes of operation are typically offered by a PDSN 141-143. These two modes of operation are often referred to as the “Simple IP” mode and the “Mobile IP” mode, both of which are described in greater detail below. In either mode, the act of an MS 101-109 moving between different PCFs 131-132 and keeping the same PDSN 141-143 is termed a “soft handoff.” The act of an MS 101-109 moving between PCFs 131-132 and also switching physical PDSNs 141-143, on the other hand, is termed a “hard handoff.” Similarly, in prior wireless communication systems, a “hard handoff” will result anytime the IP address of a PDSN 141-143 changes for a call (even if the same physical PDSN 141-143 remains in use).
In general, hard handoffs are undesirable in both the Simple IP mode and the Mobile IP mode. In the case of Simple IP, a hard handoff requires the renegotiation of all call-related access processing parameters (e.g., A11, PPP, and IP). As known by those versed in the art, renegotiation of such parameters is both time consuming and disruptive to data applications that may be running on the MS 101-109. In the case of Mobile IP, a hard handoff requires the same renegotiation of the call processing parameters as in the Simple IP case plus Mobile IP parameters. However, this procedure is less disruptive to data applications as the MS 101-109 is able to retain the same assigned IP address, and there is no disruption of the data path for the MS 101-109.
Due to the undesirability of hard handoffs, PDSNs 141-143 have typically been designed to have only a single IP address and a single corresponding physical (layer 3) interface. This is due in large part to prevent the occurrence of an “internal hard handoff,” which refers to the case where a hard handoff is thought to have occurred (and the handoff is treated as such) even though an MS 101-109 has not moved to a new PDSN 141-143. For example, in the case of a PDSN 141-143 having multiple IP addresses, an internal hard handoff may occur when an MS 101-109 roams from a first PCF 131-132 to a second PCF 132, and the second PCF 132 mistakenly uses a the wrong (i.e., a different) IP address of the same PDSN 141-143. However, the use of only a single IP address and interface for a PDSN 141-143 significantly and undesirably limits the throughput of the PDSN 141-143. That is, the throughput of the PDSN 141-143 is limited to the bandwidth provided by the single physical interface. Additionally, the use of only a single IP address and interface for a given PDSN 141-143 makes it impossible (or at least much more difficult) to provide a desired level of redundancy to protect against the effects of software or hardware failures.
Accordingly, it is desirable to provide systems and methods for using PDSNs 141-143 in a wireless communication system 100 that include multiple IP addresses, and multiple corresponding physical interfaces, while eliminating or at least substantially reducing the likelihood of internal hard handoffs.